Radio broadcast distributing system



July 5, 1927. 1,635,156

E. E. CLEMENT RADIO BROADCAST DISTRIBUTING SYSTEM Filed 001'.. 21, 1925 Patented' July 5, 1927.

UN'rl-:D s'rurssv 1,635,115@ PATENT ortica.

EDWARD E. CLEMENT, OF WASHINGTON,l DISTRICT OF COLUMBIA., ASSIGNOR T EDWARD F. A COLLADAY, 0F WASHINGTON, DISTRICT 0F COLUMBIA.

RADIO vBROADCAST DISTItIBUTING-- SYSTEM.

Applicationl led October 21, 1925; vSerial No. 63,977.

My invention relates to systemsvof radio broadcast distribution, and the present application is a continuation i-n part of my prior copending application, filed May 21, 1925, Serial No. 31,928. This invention has for its object to provide an organization for the broadcasting of intelligence in which areas, each orderly distribution, selective receiving, and secrecy may be secured, with maximum elficiency. l

' Very briefly stated, this system includes subdivision of the ultimate units or subscribers stations into local groups in local Group related to a local or regional distributing station; the grouping of these regional stations according to 'districts and relating eaclf' district group of regional stations to a district master station; the grouping of districts into divisions, which may conveniently coincide with the4 geographical standard time divisions of the country; and iially the relation of the district master stations to a central master station.

The first characteristic feature of the system is that of sending from each center to the class or order of centers next above or below it, on a fixed carrier wavefrequency or frequencies allotted'permanently to said next higher or lowerorder of stations. If we call the central master station of the entire stem A, and call the district master A stations B, the local or regional distributing stations G; and the subscribers instruments in general D, then -we maysay that A transmits to B on B frequency, B transmits to C on C frequency, 4and C transmits to D on D frequency, of the respective carrier waves. For information that goes through from A to D, or that goes through from B to D, as well as information originating with C original modulations are actually reproduced in the instruments at D, by means which will be described. 'Thesimplest way to do this is by double modulation, which also enables easy changeof carrier wave frequency at the I intermediate or relaying stations.

The second characteristic feature of this system which I shall claim therein, is the provision of means for secrec i.l e. confinlng the receptlon' of intelligi le signals yto those' who are authorized to receive them. By the userof double modulation I am enabled to produce and transmit either directly from transmitter to receiver,.or through4 a .of the receiving instrument, i. e. unauthorized or authorized.

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My invention is illustrated lin the accompanying drawings, in which:

Fig. 1 is a circuit diagram of a form of secrecy system Fig. 1a is ajmo-dification thereof.

' Fig. 2 isla circuit diagram of a relay to be used at the B and C Stations for relaying from the system of Fig. 1.

Fig. 3 is a circuit diagram of a subscribers receiving set-for use in the system of Figs. 1 and 2.

Fig. 4 is a modification of part 'of Fig. 3 showing means for reversing the phase of combined modulations.

Referring to the drawings, Fig. 1 shows an embodiment of the invention which uses double modulation' with two secondary or numeral 428 indicates a microphonencon-fnected in series with4 a suitable source o f power such as the battery 429 and the primary windings of a pair of induction coilI *160.

430 and 431 whose secondary windings ai? separately connected'to audio modulator No. l indicated by reference numeral 432 and audio modulator No. 2 indicated by reference numeral 433 respectively. The connection to co'il 430 from the microphone v428 includes a pole chan 'ngswitch' for a purpose to be explained. ach of the coils 430-431 is provided with a third winding 434--435 which third windings are connected through a transformer 436 'to a suitable source of One winding of the pair'434-435 is reversible with respect to theyother as shown. y By this means the coils mayy be broughty into the same or opposite phase relation. The modulators 432-433 are each operatively connected vwith intermediate :frequency oscilla tors 438-439 labeled onthe drawings as inalternating current 437 'of audible frequencly. v

, termediate frequency vroscillator No. 1 and inf termediate frequency oscillator No. 2respectively, which oscillators are connected individually through intermediate' modulators y 446-441 to a common short wave oscillatorv transmitter 442 having its output circuit coupled through the coupling 443 vwith the transmitting antenna 444. In operation,

,y ysound waves acting on the microphone '428 will'be electrically transferred to the No. 1

primary wave, demodulating the same'to de and No. 2 audio modulators in synchronism erated by the oscillators 438 and 439 w ich intermediate frequency vwaves are in yturn modulated through 'their'respective No. 1 and No. 2 modulators onto the short Wave generated by the oscillator 442. ,Y This yshort wave carrying both the yintermediate frekquency waves with their 'modulations is radiated out from the transmitting antenna 444 as'a double modulated wave. f l

For relayingy this double. modulated wave without passing through the audio stage, thev relay apparatus of Fig. 2 is provided. Thisr consists generally of means for receivingthe tect the twov different intermediate fre-v. quency waves and again modulating these two waves onto another short primary wave i mediate frequency wave'sfborne by the pri- .maryrradlated wave are relayedentv e 69- of a frequency different from and non-interfering with the received wave. Referring more in detail`v to the elements constituting this system, the reference numeral.445 indicat-es the receiving antenna coupled through a coupler to a first detector apparatus 447, the input circuit of which is tuned` to the primary wave. This detector 447 is a'rranged to detect out both intermediate frequency waves andput them onto its output circuit 448 which is connected as shown to two filter couplers 449 and 45() tuned, respective1y,"to the first and second intermediate frequency waves. The filter couplers 441`- and 45'0 are'connected to the input terminals of the. No. 1 and No. 2 intermediate frequency modulators 451 and 452 the output terminals of which connect to the input side of a short wave oscillator transmitter 453 which has its output circuit coupled tiirough the coupler 454 to the` transmitting antenna 455', the oscillator 453 being adjusted to generate a wave of a frequency dierent from and non-interfering witlrthat of the received wave. Thus', in, operation,v .the- 'two inter- Y loud speaker or the like. In operation the 'double modulated wave'received on the an-y ond primary; wave transmitted from the transmitting antenna 45.5 without demodula--. tion. The relay system of Fig.' 2 is the same for both the intermediate or relay stations, that is the B and C stations, with the exception that their oscilla-tor transmitters are, of 1purse, adjusted to transmit on different and ion-interfering frequencies.

The subscribers apparatus for receiving the special double modulated' wave trans-r mitted from its local C station is indicated diagrammatically in Fig. 3 in which the receiving antenna v4:56 is shown coupled throughia rtuned coupling circuit 457 with a first detector apparatus 458, which detects out both the intermediate frequency wavesand passes them Aon through its output circuit 45`9to the two filter couplers 460k andv 461 tuned to the first intermediate frequency andy to the second intermediate frequency respectively. The filter couplers 460-461 are connected to the input circuits of second detectors 462-463 whose ,output cirv cuits are in turn*y connected to the primary coils 464 and 465 respectively, of transformer 466 the secondary winding of ywhich v includes a telephone receiver vset 467 which, it is to be understood, is typical of any suitl able form kof -telephone receiver such as a' tennav456` is :first demodulated bythe first detector 458 to ydetect outV the two different intermediate vfrequency waves the first of vwhich passes through the filter cou'pler V460 y10u .y

and the second detector 462, while the second intermediate frequency wave' passes through filter coupler 461 tothe second detector 463. Each of the two second detectors operates to detect out the desired audio modulations togetherwith the obscuring hum and passes the same -through its primary windin s to the induction co1l`or transformer 466 t e two primary windings beingso related by means 'of pole changing switch 110 468 as to augment each i`other as to the de-l sired audio modulations, while the modulations representing the obscuring hum are depha'sed so thatthey will neutralize each otherin the common magnetic' circuit of the l11-5 transformer and only the v desired modulations will be heard in the receiver 467.

It' will be noted that Vby reversing the connections of one of the secondary windings of the transformer 466 as by means of switch Amicrophone at the sending station will be cenoelledout 9; neutralized and so will not 139 be audible. rl`hus, if at.the sending staltion (Fig. 1) a second microphone` is used to vary the current iowin the third windings 434 and 435 of the modulating transformers, in place of source of alternating current 437, matter beine' ,picked up by one microphone' may be used to obscure or render unintelligiblethe matter picked upby the other. In practice, this enables both intermediate frequencies to be usefully emplo'yed without lessening the secrecy feat-ure. For example, the two sets ofv modulations may be constituted of-two different program numbers in the same program, or in the case of a son or spoken part, the same item rendered -1 n different languages. The advantage attained by this use of the system of tation. The dierent modulations in phase and out of phase ma be imposed on inter- Figs. 1, 2 and 3, is that the combination of vthe two fnequenciesis made to'subservetwo functions, at the same time, namely, .secrecy and selection.

' It is to be understood Ithat the .foregoing ldescription and specific illustration accomi panyingthe same are used for purposes of definition and explanation but not of limimediate wavesmodu ated in turn on 'separately generated primary carrier waves, and in general any change necessary or desirable for carrying out the principle of this' invcntion is contemplated jas within the scope and purview thereof. Thus, two or more separate secondary or' intermediate -frequency carrier waves may each -be modulated with a dierent audio signal, and may valso carry an obscu-ring tone or hum, all

of these being modulated in turn on a single short wave carrier or on several carriers of the same frequency. \This` arrangement will obscure the signals completely. However, a separate intermediate frequency carrier to be used as a neutralizer of hum, will also be modulated with the same hum, in phase, and this will then also be modulated on the primary carrier.v Anyunauthorized receivin station, Whether using single detection or ouble detection, will get only hum; but an authorized receiving station equipped as herein described, and i lustrated for example in Fig. 3, will be able -to dephase the hum derived from the balancing wave, and by combiningthis with any selected one of the obscured signal-waves, can neutralize the hum thereon and receive the signal. Selective equipment for this pur'- f pose-is shown in Fig. 4.

It is to-be further understood that in the rdiagrammatic showing herein no attempt .fhas been made to include the details of working circuits; and such necessary pieces of apparatus asyamplifiers, filters, filter networks, and phase adjusting means, all of which are well-known in the. art, are con-- templated in the practice Qt the invention,

I claim- 1. The method of secret radio transmission l which consists in imposing the same signal modulations on two different intermediate frequency carrier waves both modulated onl one high frequency primary carrier wave,

said signal modulations being in opposite phase" on the dierent intermediate.A waves so as toneutralize each other for detection alone, and at a receiving station separately detecting the opposite audio modulations wave, detecting out both modulated intermediate Vwaves and remodulating the same together on a second prlmary wave d1fferent from and non-interfering with the .first primary wave.

3. vA secrecy radi/o transmission system` phase, means for modulating a second set.

of audio 'signal Waves in opposite phase, on the diiferentl sets o f oscillations, means for generating relatively high or radio fraquency oscillations, means for modulating both said lrelatively low frequency oscillations on said high frequency oscillations, and means for radiating the said high frequency oscillations.

, 5. A secrecy radio broadcast system comprising means'for generating two sets of relatively low frequency 'oscillations of dif-- ferent frequencies, means for modulating both' said relatively low frequency oscillations with two different sets of audio modulations the rst 1n phase on both sets of' 0scillations and the second in opposite phase on the different sets of oscillations, means for generating and radiating oscillations of relatively high frequency, means for modulating both said relatively low frequency oscillations on said relatively high frequency.

oscillations and receiving means comprising means for receiving high frequency oscillations, a first detector 'for demod-ulating said high frequency waves to detect said low frequency waves, a pair of filter circuits' for segregating said low frequency Waves, a' pair 0f Sedona detectors? 0.11.9 for each lter cir- Alations the first in phase on both sets o'fmos.-

cillations and the second'in opposite phase on the different sets of oscillations, means for generating and radiating oscillations of relatively high' frequency, means for modulating both said relatively low frequency oscillations on said relatively high frequency l oscillations and receivingmeans comprising means for receivngfhigh frequency oscillations, a first detector for demodulating said high frequency waves to detect said low frequency Waves, a pair of filter circuits for segregating said low frequency Waves, a pair of second detectors, one for each filter circuit arranged to detect the audio modu- .1a-tions carried bythe respective setsl of low frequency Waves and means for combining audio modulations thus detected, together with means for translating said audio modulations into sound Waves.

7. A. secrecy system of radio broadcast distribution comprising a transmitter for` transmitting a `double modulated primary Wave modulated With two different intermediate frequencywaves, means for modulating a,

set of audio Waves on both said intermediate Waves 1n phase, means for modulatlng a second set of audio waves 'on both said iny termediate Waves in opposite phase, a relay transmitter arranged to receive said primary Wave and retransmit both said intermediate Waves on another primary wave different from and non-interfering with the' first primary Wave, and receiving stations grouped 'around each said relay-station in a localarea and arranged to detect and combine both said sets of audio waves.

In testimony whereof I hereuntoalii; my

signature.

EDWARD E. CLEMENT.l 

